# STRELA

Investigation of charge-exchange processes in the deuteron-proton collisions

The experiment STRELA is proposed to study the spin dependent part of the nucleon scattering amplitude in the np → pn charge-exchange process at the Nuclotron deuteron beam. It is planned to measure the two proton production cross section at small momentum transfers in the dp interactions in the range of the deuteron momentum from 3.0 GeV/c to 4.0 GeV/c.

### Spokesmen

• Glagolev Victor Victorovich
• Martinska Gabriela
• Piskunov Nikolay Mikhailovich

### Physics goal

The possibility to get additional information about the amplitude of the elementary np → pn charge-exchange reaction by means of the charge-exchange process dp → (pp)n from the experiments with unpolarized deuteron was emphasized by A. B. Migdal[1] and I. Y. Pomeranchuk[2].

Simplified versions of these two processes in the framework of the impulse approximation are shown in figure (a) the charge-exchange process and (b) the reaction, i.e. charge-exchange one on the simplest nucleus - the deuteron. Vertical arrows stand for the nucleon spins with respect to an arbitrary axis of quantization. In the first case (a) both spin orientations are allowed while in the second one (b) at small angle scattering (spatial symmetry) due to the produced charged symmetry (two protons move in the very forward direction with small relative momentum) the reaction can proceed only if the scattered proton spin flips (caused by the Pauli exclusive principle). So, the deuteron behaves itself as a spin filter. Different experimental attempts have been made, including bubble chambers, to estimate the spin dependent part of the elementary np → pn process from dp scattering.

The mathematical formalism for exchange scattering was developed, for example by L. I. Lapidus[3] and N. W. Dean[4] and others. The differential cross section for the charge-exchange process on the deuteron can be written as:

$(d\sigma/dt)_{dp \rightarrow (pp)n} = \bigl[1 - F_d(t)\bigr]\,(d\sigma/dt)^{SI}_{np \rightarrow pn} +\, \bigl[1 - 1/3\,F_d(t)\bigr]\,(d\sigma/dt)^{SD}_{np \rightarrow pn}$

where $F_d(t)$ denotes the deuteron form factor, $(d\sigma/dt)^{SI}_{np \rightarrow pn}$ or $(d\sigma/dt)^{SD}_{np \rightarrow pn}$ the spin independent (SI) or spin dependent (SD) part of the differential cross section, respectfully. At zero momentum transfers $(t = 0)$ when $F_d(0) = 1$ this expression becomes:

$(d\sigma/dt)_{dp \rightarrow (pp)n} = 2/3\,(d\sigma/dt)^{SD}_{np \rightarrow pn}$

i.e. the differential cross section is determined by the spin flip part of the charge-exchange process. The importance of the spin state ratios is given by the fact that it allows one to determine the nature of interference effects in the two proton distributions.

References :
1. A.B. Migdal, Zh. Eksp. Teor. Fiz. (in Russian) 28, 3, (1955)
2. I.Y. Pomeranchuk, Dokl. Akad. Nauk (in Russian) LXXVIII, 249, (1951)
3. L.I. Lapidus, Zh. Eksp. Teor. Fiz. (in Russian) 32, 1437, (1957)
4. N.W. Dean, Phys. Rev. D 5, 2832, (1972)